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Chung King Law - One of the best experts on this subject based on the ideXlab platform.
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On the determination of laminar Flame speed from low-pressure and super-Adiabatic propagating spherical Flames
Proceedings of the Combustion Institute, 2019Co-Authors: Faghih, Jialong Huo, Zhuyin Ren, Chung King LawAbstract:Abstract The outwardly propagating spherical Flame (OPF) method is popularly used to measure the laminar Flame speed (LFS). Recently, great efforts have been devoted to improving the accuracy of the LFS measurement from OPF. In the OPF method, several assumptions are made. For examples, the burned gas is assumed to be static and in chemical equilibrium. However, these assumptions may not be satisfied under certain conditions. Here we consider low-pressure and super-Adiabatic propagating spherical Flames, for which chemical non-equilibrium exists and the burned gas may not be static. The objective is to assess the chemical non-equilibrium effects on the accuracy of LFS measurement from the OPF method. Numerical simulations considering detailed chemistry and transport are conducted. Stoichiometric methane/air Flames at sub-atmospheric pressures and methane/oxygen Flames at different equivalence ratios are considered. At low pressures, broad heat release zone is observed and the burned gas cannot quickly reach the Adiabatic Flame Temperature, indicating the existence of chemical non-equilibrium of burned gas. Positive flow in the burned gas is identified and it is shown to become stronger at lower initial pressure. Consequently, the LFS measurement from OPF at low pressures is not accurate if the burned gas is assumed to be static and at chemical equilibrium. For super-Adiabatic spherical Flames, the burned gas speed is found to be negative due to the local Temperature overshoot at the Flame front. Such negative speed of burned gas can also reduce the accuracy of LFS measurement. It is recommended that the direct method measuring both Flame propagation speed and flow speed of unburned gas should be used to determine the LFS at low pressures or for mixtures with super-Adiabatic Flame Temperature.
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laminar Flame propagation in supercritical hydrogen air and methane air mixtures
Proceedings of the Combustion Institute, 2019Co-Authors: Wenkai Liang, Chung King LawAbstract:Abstract The propagation of laminar hydrogen/air and methane/air Flames in supercritical conditions was computationally simulated for the planar Flame configurations, incorporating descriptions of supercritical thermodynamics and transport as well as high-pressure chemical kinetics. The inaccuracies associated with the use of ideal gas assumptions for various components of the supercritical description were systematically assessed with progressively more complete formulation. Results show that, for hydrogen/air Flames, the laminar Flame speeds at high pressures increase due to the non-ideal equation of state (EoS), and is mainly due to the density modification of the initial mixture. Including the thermodynamic properties of heat capacity reduces the Flame speed because of the correspondingly reduced Adiabatic Flame Temperature. Transport properties were found to have small effect because of the inherent insensitivity of the laminar burning rate to variations in the transport properties. For methane/air Flames, the use of recently reported high-pressure chemical kinetics considerably affects the laminar Flame speed, even for the same Flame Temperature.
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on the off stoichiometric peaking of Adiabatic Flame Temperature
Combustion and Flame, 2006Co-Authors: Chung King Law, Atsushi MakinoAbstract:The characteristic rich shifting of the maximum Adiabatic Flame Temperature from the stoichiometric value for mixtures of hydrocarbon and air is demonstrated to be caused by product dissociation and hence reduced amount of heat release. Since the extent of dissociation is greater on the lean side as a result of the stoichiometry of dissociated products, the peaking occurs on the rich side. The specific heat per unit mass of the mixture is shown to increase monotonically with increasing fuel concentration, and as such tends to shift the peak toward the lean side. It is further shown that this is the cause for the lean shifting of the Adiabatic Flame Temperature of oxidizer-enriched mixtures of N{sub m}H{sub n} and F{sub 2} and of NH{sub 3} and O{sub 2}, with various amounts of inert dilution, even though their maximum heat release still peaks on the rich side. (author)
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detailed oxidation kinetics and Flame inhibition effects of chloromethane
Combustion and Flame, 1996Co-Authors: Hai Wang, T O Hahn, Chihjen Sung, Chung King LawAbstract:A comprehensive experimental and numerical study has been performed on the detailed oxidation kinetics and the Flame inhibition effects of chloromethane, with an emphasis on the isolation of the Temperature and chemical effects caused by substitution of methane in the fuel by chloromethane. The experimental efforts involved the determination of laminar burning velocities for a series of fuel mixtures of different ratios of chloromethane to methane, but with a fixed ratio of total fuel to oxygen (and air). The thermal and chemical effects were isolated by comparing the laminar burning velocities obtained with the Adiabatic Flame Temperature uncompensated with the substitution of methane by chloromethane, versus those obtained with fixed Adiabatic Flame Temperature achieved by replacing nitrogen in air with an equal amount of argon. The experimental results indicate that Temperature reduction due to increased chloromethane substitution is a significant factor for the reduction in the laminar burning velocity. Furthermore, when the results at a fixed Flame Temperature were examined on the basis of the mass burning rate, which is the eigenvalue for laminar Flame propagation, the response was found to be insensitive to the chloromethane concentration in the mixture. This implies the possibility of a corresponding insensitivity to the chlorine Flame chemistry. Concurrently, a detailed reaction mechanism of chloromethane/methane oxidation was compiled and validated against literature data from shock tube to flow reactor studies. Numerical simulation of the present experimental situation was then performed. The numerical results were found to be in close agreement with the current experimental findings.
Thierry Poinsot - One of the best experts on this subject based on the ideXlab platform.
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effects of hydrogen and steam addition on laminar burning velocity of methane air premixed Flame experimental and numerical analysis
International Journal of Hydrogen Energy, 2012Co-Authors: Toufik Boushaki, Yannick Dhue, Laurent Selle, Bernard Ferret, Thierry PoinsotAbstract:Effects of hydrogen enrichment and steam addition on laminar burning velocity of methaneeair premixed Flame were studied both experimentally and numerically. Measurements were carried out using the slot burner method at 1 bar for fresh gases Temperatures of 27 °C and 57 °C and for variable equivalence ratios going from 0.8 to 1.2. The hydrogen content in the fuel was varied from 0% to 30% in volume and the steam content in the air was varied from 0 to 112 g/kg (0e100% of relative humidity). Numerical calculations were performed using the COSILAB code with the GRI-Mech 3.0 mechanism for one-dimensional premixed Flames. The calculations were implemented first at room Temperature and pressure and then extended to higher Temperatures (up to 917 K) and pressures (up to 50 bar). Measurements of laminar burning velocities of methanee hydrogeneair and methaneeairesteam agree with the GRI-Mech calculations and previous measurements from literature obtained by different methods. Results show that enrich- ment by hydrogen increases of the laminar burning velocity and the Adiabatic Flame Temperature. The addition of steam to a methaneeair mixture noticeably decreases the burning velocity and the Adiabatic Flame Temperature. Modeling shows that isentropic compression of fresh gases leads to the increase of laminar burning velocity.
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asymptotic and numerical study of diffusion Flames with variable lewis number and finite rate chemistry
Combustion and Flame, 1996Co-Authors: Benedicte Cuenot, Thierry PoinsotAbstract:Abstract We use an asymptotic method (from Linan [21]) to derive analytical expressions for the profiles of all thermodynamic and chemical quantities of a diffusion Flame with variable density, nonuniform Lewis number and finite rate chemistry, and for different configurations (unsteady unstrained, steady strained and unsteady strained Flames). The accuracy of results is checked using numerical simulations with the same chemical and transport models. These results are then used to quantify the effects of finite rate chemistry and different Lewis numbers on the Flame structure. In particular, we show that the Adiabatic Flame Temperature is not always a monotone function of the Lewis numbers, and we give simple expressions to predict the total heat release when the fuel and oxidizer Lewis numbers are different.
Yin Wang - One of the best experts on this subject based on the ideXlab platform.
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comparison of direct combustion in a circulating fluidized bed system and decoupling combustion in a dual fluidized bed system for distilled spirit lees
Energy & Fuels, 2016Co-Authors: Zhennan Han, Xi Zeng, Changbin Yao, Yin WangAbstract:At present in China, a fluidized bed combustor is not suitable to treat a high-water-containing (30–60 wt %) industrial biomass residue, such as distilled spirit lees (DSL), which can cause a low bed Temperature and inflammation retardation. Our previous fundamental studies showed that the so-called dual fluidized bed gasification decoupling combustion technology (or decoupling combustion for short) can ensure the highly efficient and stable combustion for high-water-containing biomass fuel and lower NOx emission as well. In this study, the combustion characteristics of DSL in a circulating fluidized bed (CFB) system and a dual fluidized bed (DFB) system will be examined and compared systematically. For direct combustion of DSL in a CFB system, the high moisture of 30 wt % decreased the bottom Temperature of the combustor significantly and brought in unstable combustion, thus leading to s large amount of auxiliary fuel (such as coal) needed to raise the Temperature to reach an Adiabatic Flame Temperature ...
Mohamed A Habib - One of the best experts on this subject based on the ideXlab platform.
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characteristics of oxyfuel combustion in lean premixed multihole burners
Energy & Fuels, 2019Co-Authors: Mansur Aliyu, Medhat A Nemitallah, Mohamed A Habib, Ahmed A Abdelhafez, S A M Said, Ibrahim B MansirAbstract:This paper presents the results of an experimental investigation of combustion characteristics of nonswirl CH₄/CO₂/O₂ Flames under atmospheric pressure in a lean-premixed multihole burner’s gas-turbine model combustor. The CO₂ and O₂ are well premixed and then channeled to a test rig, which is made up of a 2 in. diameter 1 m long pipe to premix the fuel and oxidizers before getting to the multihole burner. The burner consists of main holes and subholes that prevent flashbacks that may lead to rig explosion. The burner imparts jet to the premixed measured composition of CH₄/CO₂/O₂. The results indicated that the Adiabatic Flame Temperature (Tₐd) is a strong controlling parameter in quantifying the stability map and combustor Flame shape; variation in oxygen fraction and equivalence ratio influence the Flame shape, whereas the equivalence ratio (ϕ) is the major controlling parameter of Temperature distribution within the combustor. The results also indicated that the stability map does not follow the lines of constant power density, mass flow rate of the mixture (mₘᵢₓ), and Reynolds number (Re).
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combustion behavior and stability map of hydrogen enriched oxy methane premixed Flames in a model gas turbine combustor
International Journal of Hydrogen Energy, 2018Co-Authors: Binash Imteyaz, Medhat A Nemitallah, Ahmed Abdelhafez, Mohamed A HabibAbstract:Abstract The article describes an experimental study and comparison of the combustion behavior and determines the stability map of turbulent premixed H2-enriched oxy-methane Flames in a model gas turbine combustor. Static stability limits, in terms of flashback and blow-out limits, are recorded over a range of hydrogen fraction (HF) at a fixed oxygen fraction (OF) of 30% and a particular inlet bulk velocity, and the results are compared with the non-enriched case (HF = 0%). The static stability limits are also recorded for different inlet bulk velocity (4.4, 5.2, and 6 m/s) and the results are compared to explore the effect of flow dynamics on operability limits of H2-enriched Flames. The stability maps are presented as a function of equivalence ratio (0.3–1.0) and HF (0%–75%) plotted on the contours of Adiabatic Flame Temperature (AFT), power density (PD), inlet Reynolds number (Re) and reacting mixture mass flow rate ( m ˙ ) to understand the physics behind flashback and blow-out phenomena. The results indicated that both the flashback and blow-out limits tend to move towards the leaner side with increasing HF due to the improved chemical kinetics. The stability limits are observed to follow the Reynolds number indicating its key role in controlling Flame static stability limits. The results showed that H2 enrichment is effective in the zone from HF = 20% up to HF = 50%, and O2 enrichment is also effective in a similar zone from OF = 20% up to 50%, with wider stability boundaries for H2 enrichment. Axial and radial Temperature profiles are presented to explore the effect of HF on the progress of chemical reactions within the combustor and to serve as the basis for validation of numerical models. Flame shapes are recorded using a high-speed camera and compared for different inlet velocities to explore the effects of H2-enrichment and equivalence ratio on Flame stability. The equivalence ratio at which a transition of Flame stabilization from the inner shear layer (ISL) to the outer recirculation zone (ORZ) occurs is determined for different inlet bulk velocities. The value of the transition equivalence ratio is found to decrease while increasing the inlet bulk velocity. Flame shapes near flashback limit, as well as near blow-out limit, are compared to explore the mechanisms of Flame extinctions. Flame shapes are compared at fixed Adiabatic Flame Temperature, fixed inlet velocity and fixed flow swirl to isolate their effects and investigate the effect of kinetic rates on Flame stability. The results showed that the Adiabatic Flame Temperature does not govern the Flame static stability limits.
Zhennan Han - One of the best experts on this subject based on the ideXlab platform.
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comparison of direct combustion in a circulating fluidized bed system and decoupling combustion in a dual fluidized bed system for distilled spirit lees
Energy & Fuels, 2016Co-Authors: Zhennan Han, Xi Zeng, Changbin Yao, Yin WangAbstract:At present in China, a fluidized bed combustor is not suitable to treat a high-water-containing (30–60 wt %) industrial biomass residue, such as distilled spirit lees (DSL), which can cause a low bed Temperature and inflammation retardation. Our previous fundamental studies showed that the so-called dual fluidized bed gasification decoupling combustion technology (or decoupling combustion for short) can ensure the highly efficient and stable combustion for high-water-containing biomass fuel and lower NOx emission as well. In this study, the combustion characteristics of DSL in a circulating fluidized bed (CFB) system and a dual fluidized bed (DFB) system will be examined and compared systematically. For direct combustion of DSL in a CFB system, the high moisture of 30 wt % decreased the bottom Temperature of the combustor significantly and brought in unstable combustion, thus leading to s large amount of auxiliary fuel (such as coal) needed to raise the Temperature to reach an Adiabatic Flame Temperature ...